Showing papers by "Jesús Falcón-Barroso published in 2020"

The X-shooter Spectral Library (XSL): Data release 2

Abstract: We present the second data release (DR2) of the X-shooter Spectral Library (XSL), which contains all the spectra obtained over the six semesters of that program. This release supersedes our first data release from Chen et al. (2014, A&A, 565, A117), with a larger number of spectra (813 observations of 666 stars) and with a more extended wavelength coverage as the data from the near-infrared arm of the X-shooter spectrograph are now included. The DR2 spectra then consist of three segments that were observed simultaneously and, if combined, cover the range between ∼300 nm and ∼2.45 μ m at a spectral resolving power close to R = 10 000. The spectra were corrected for instrument transmission and telluric absorption, and they were also corrected for wavelength-dependent flux-losses in 85% of the cases. On average, synthesized broad-band colors agree with those of the MILES library and of the combined IRTF and Extended IRTF libraries to within ∼1%. The scatter in these comparisons indicates typical errors on individual colors in the XSL of 2−4%. The comparison with 2MASS point source photometry shows systematics of up to 5% in some colors, which we attribute mostly to zero-point or transmission curve errors and a scatter that is consistent with the above uncertainty estimates. The final spectra were corrected for radial velocity and are provided in the rest-frame (with wavelengths in air). The spectra cover a large range of spectral types and chemical compositions (with an emphasis on the red giant branch), which makes this library an asset when creating stellar population synthesis models or for the validation of near-ultraviolet to near-infrared theoretical stellar spectra across the Hertzsprung-Russell diagram.

Insights into formation scenarios of massive early-type galaxies from spatially resolved stellar population analysis in CALIFA

Abstract: We perform spatially resolved stellar population analysis for a sample of 69 early-type galaxies (ETGs) from the CALIFA integral field spectroscopic survey, including 48 ellipticals and 21 S0's. We generate and quantitatively characterize profiles of light-weighted mean stellar age and metallicity within $\lesssim 2R_e$, as a function of radius and stellar-mass surface density $\mu_*$. We study in detail the dependence of profiles on galaxies' global properties, including velocity dispersion $\sigma_e$, stellar mass, morphology. ETGs are universally characterized by strong, negative metallicity gradients ($\sim -0.3\,\text{dex}$ per $R_e$) within $1\,R_e$, which flatten out moving towards larger radii. A quasi-universal local $\mu_*$-metallicity relation emerges, which displays a residual systematic dependence on $\sigma_e$, whereby higher $\sigma_e$ implies higher metallicity at fixed $\mu_*$. Age profiles are typically U-shaped, with minimum around $0.4\,R_e$, asymptotic increase to maximum ages beyond $\sim 1.5\,R_e$, and an increase towards the centre. The depth of the minimum and the central increase anti-correlate with $\sigma_e$. A possible qualitative interpretation of these observations is a two-phase scenario. In the first phase, dissipative collapse occurs in the inner $1\,R_e$, establishing a negative metallicity gradient. The competition between the outside-in quenching due to feedback-driven winds and some form of inside-out quenching, possibly caused by central AGN feedback or dynamical heating, determines the U-shaped age profiles. In the second phase, the accretion of ex-situ stars from quenched and low-metallicity satellites shapes the flatter stellar population profiles in the outer regions.

Kinematic signatures of nuclear discs and bar-driven secular evolution in nearby galaxies of the MUSE TIMER project

Abstract: The central regions of disc galaxies hold clues to the processes that dominate their formation and evolution. To exploit this, the TIMER project has obtained high signal-to-noise and spatial resolution integral-field spectroscopy data of the inner few kpc of 21 nearby massive barred galaxies, which allows studies of the stellar kinematics in their central regions with unprecedented spatial resolution. We confirm theoretical predictions of the effects of bars on stellar kinematics and identify box/peanuts through kinematic signatures in mildly and moderately inclined galaxies, finding a lower limit to the fraction of massive barred galaxies with box/peanuts at ∼62%. Further, we provide kinematic evidence of the connection between barlenses, box/peanuts, and bars. We establish the presence of nuclear discs in 19 galaxies and show that their kinematics are characterised by near-circular orbits with low pressure support and that they are fully consistent with the bar-driven secular evolution picture for their formation. In fact, we show that these nuclear discs have, in the region where they dominate, larger rotational support than the underlying main galaxy disc. In addition, we define a kinematic radius for the nuclear discs and show that it relates to bar radius, ellipticity and strength, and bar-to-total ratio. Comparing our results with photometric studies of galaxy bulges, we find that careful, state-of-the-art galaxy image decompositions are generally able to discern nuclear discs from classical bulges if the images employed have high enough physical spatial resolution. In fact, we show that nuclear discs are typically identified in such image decompositions as photometric bulges with (near-)exponential profiles. However, we find that the presence of composite bulges (galaxies hosting both a classical bulge and a nuclear disc) can often be unnoticed in studies based on photometry alone and suggest a more stringent threshold to the Sersic index to identify galaxies with pure classical bulges.

The inside-out formation of nuclear discs and the absence of old central spheroids in barred galaxies of the TIMER survey

Abstract: The centres of disc galaxies host a variety of structures built via both internal and external processes. In this study, we constrain the formation and evolution of these central structures, in particular nuclear rings and nuclear discs, by deriving maps of mean stellar ages, metallicities and [$\alpha$/Fe] abundances. We use observations obtained with the MUSE integral-field spectrograph for the TIMER sample of 21 massive barred galaxies. Our results indicate that nuclear discs and nuclear rings are part of the same physical component, with nuclear rings constituting the outer edge of nuclear discs. All nuclear discs in the sample are clearly distinguished based on their stellar population properties. As expected in the picture of bar-driven secular evolution, nuclear discs are younger, more metal-rich, and show lower [$\alpha$/Fe] enhancements, as compared to their immediate surroundings. Moreover, nuclear discs exhibit well-defined radial gradients, with ages and metallicities decreasing, and [$\alpha$/Fe] abundances increasing with radius out to the nuclear ring. Often, these gradients show no breaks from the edge of the nuclear disc until the centre, suggesting that these structures extend to the very centres of the galaxies. We argue that continuous (stellar) nuclear discs may form from a series of bar-built (initially gas-rich) nuclear rings that grow in radius, as the bar evolves. In this picture, nuclear rings are simply the (often) star-forming outer edge of nuclear discs. Finally, by combining our results with those from a accompanying kinematic study, we do not find evidence for the presence of large, dispersion-dominated components in the centres of these galaxies. This could be a result of quiet merger histories, despite the large galaxy masses, or perhaps high angular momentum and strong feedback processes preventing the formation of these kinematically hot components.

Inside-out formation of nuclear discs and the absence of old central spheroids in barred galaxies of the TIMER survey

Abstract: The centres of disc galaxies host a variety of structures built via both internal and external processes. In this study, we constrain the formation and evolution of these central structures, in particular, nuclear rings and nuclear discs, by deriving maps of mean stellar ages, metallicities, and [α/Fe] abundances. We use observations obtained with the MUSE integral-field spectrograph for the TIMER sample of 21 massive barred galaxies. Our results indicate that nuclear discs and nuclear rings are part of the same physical component, with nuclear rings constituting the outer edge of nuclear discs. All nuclear discs in the sample are clearly distinguished based on their stellar population properties. As expected in the picture of bar-driven secular evolution, nuclear discs are younger, more metal-rich, and exhibit lower [α/Fe] enhancements, as compared to their immediate surroundings. Moreover, nuclear discs exhibit well-defined radial gradients, with ages and metallicities decreasing, and [α/Fe] abundances increasing with radius out to the nuclear ring. Often, these gradients show no breaks from the edge of the nuclear disc up through the centre, suggesting that these structures extend to the very centres of galaxies. We argue that continuous (stellar) nuclear discs may form from a series of bar-built (initially gas-rich) nuclear rings that expand in their radius as the bar evolves. In this picture, nuclear rings are simply the (often) star-forming outer edge of nuclear discs. Finally, by combining our results with those taken from a accompanying kinematic study, we do not find evidence for the presence of large, dispersion-dominated components in the centres of these galaxies. This could be a result of quiet merger histories, despite the large galaxy masses, or, perhaps, due to high angular momentum and strong feedback processes preventing the formation of these kinematically hot components.

Kinematic signatures of nuclear discs and bar-driven secular evolution in nearby galaxies of the MUSE TIMER project

Abstract: The central regions of disc galaxies hold clues to the processes that dominate their formation and evolution. The TIMER project has obtained high signal-to-noise and spatial resolution integral-field spectroscopy data of the inner few kpc of 21 nearby massive barred galaxies, allowing studies of the stellar kinematics with unprecedented spatial resolution. We confirm theoretical predictions of the effects of bars on stellar kinematics, and identify box/peanuts through kinematic signatures in mildly and moderately inclined galaxies, finding a lower limit to the fraction of massive barred galaxies with box/peanuts at ~62%. Further, we provide kinematic evidence of the connection between barlenses, box/peanuts and bars. We establish the presence of nuclear discs in 19 galaxies and show that their kinematics are characterised by near-circular orbits with low pressure support, and are consistent with the bar-driven secular evolution picture for their formation. In fact, we show that these nuclear discs have, in the region where they dominate, larger rotational support than the underlying main galaxy disc. We define a kinematic radius for the nuclear discs and show that it relates to bar radius, ellipticity and strength, and bar-to-total ratio. Comparing our results with photometric studies, we find that state-of-the-art galaxy image decompositions are able to discern nuclear discs from classical bulges, if the images employed have enough physical spatial resolution. In fact, we show that nuclear discs are typically identified in such image decompositions as photometric bulges with (near-)exponential profiles. However, we find that the presence of composite bulges (galaxies hosting both a classical bulge and a nuclear disc) can often be unnoticed in studies based on photometry alone, and suggest a more stringent threshold to the Sersic index to identify galaxies with pure classical bulges.

The Fornax Deep Survey with VST. VIII. Connecting the accretion history with the cluster density

Abstract: Context. This work is based on deep multi-band (g, r, i ) data from the Fornax Deep Survey with the VLT Survey Telescope (VST). We analyse the surface brightness profiles of the 19 bright early-type galaxies (ETGs; m B ≤ 15 mag) inside the virial radius of the Fornax cluster (R vir ∼ 0.7 Mpc), in the mass range 8 × 108 ≤ M * ≤ 1.2 × 1011 M ⊙ .Aims. The main aim of this work is to identify signatures of accretion onto galaxies by studying the presence of outer stellar haloes and to understand their nature and occurrence. Our analysis also provides a new and accurate estimate of the intra-cluster light inside the virial radius of Fornax.Methods. We performed multi-component fits to the azimuthally averaged surface brightness profiles available for all sample galaxies. This allows us to quantify the relative weight of all components in the galaxy structure that contribute to the total light. In addition, we derived the average g − i colours in each component identified by the fit, as well as the azimuthally averaged g − i colour profiles, to correlate them with the stellar mass of each galaxy and the location inside the cluster.Results. We find that in the most massive (1010 ≤ M ≤ 1011 M ⊙ ) and reddest ETGs the fraction of light in, probably accreted, haloes (50%–90%) is much larger than in the other galaxies. All of these are located in the high-density region of the cluster (≤0.4R vir ∼ 0.3 Mpc), belonging to the north-south clump (NS clump). Less massive galaxies (109 ≤ M ≤ 1010 M ⊙ ) have an accreted mass fraction that is lower than 30%, have bluer colours, and reside in the low-density regions of the cluster. The colour profiles of the ETGs with the largest accreted mass fraction tend to flatten in the outskirts of the galaxy, that is beyond the transition radius from the central in situ to the ex situ accreted component. Inside the virial radius of the cluster (∼0.7 Mpc), the total luminosity of the intra-cluster light, compared with the total luminosity of all cluster members (bright galaxies and dwarfs), is about 34%.Conclusions. Inside the Fornax cluster there is a clear correlation between the amount of accreted material in the stellar haloes of galaxies and the density of the environment in which those galaxies reside. By comparing this quantity with theoretical predictions and previous observational estimates, there is a clear indication that the driving factor for the accretion process is the total stellar mass of the galaxy, which agrees with the hierarchical accretion scenario. Massive galaxies in the NS clump, with the largest accreted mass fractions, went through pre-processing in a group environment before this group merged with the main cluster early on. At the present epoch of the Fornax assembly history, these galaxies are the major contribution to the stellar density in the core of the cluster.

The Fornax 3D project: Globular clusters tracing kinematics and metallicities

Abstract: Globular clusters (GCs) are found ubiquitously in massive galaxies and due to their old ages, they are regarded as fossil records of galaxy evolution. Spectroscopic studies of GC systems are often limited to the outskirts of galaxies, where GCs stand out against the galaxy background and serve as bright tracers of galaxy assembly. In this work, we use the capabilities of the Multi Unit Explorer Spectrograph (MUSE) to extract a spectroscopic sample of 722 GCs in the inner regions (≲3 R eff ) of 32 galaxies in the Fornax cluster. These galaxies were observed as part of the Fornax 3D project, a MUSE survey that targets early and late-type galaxies within the virial radius of Fornax. After accounting for the galaxy background in the GC spectra, we extracted line-of-sight velocities and determined metallicities of a sub-sample of 238 GCs. We found signatures of rotation within GC systems, and comparing the GC kinematics and that of the stellar body shows that the GCs trace the spheroid of the galaxies. While the red GCs prove to closely follow the metallicity profile of the host galaxy, the blue GCs show a large spread of metallicities but they are generally more metal-poor than the host.

The X-Shooter Spectral Library (XSL): Data Release 2

Abstract: We present the second data release (DR2) of the X-Shooter Spectral Library (XSL), which contains all the spectra obtained over the six semesters of that program. This release supersedes our first data release from Chen et al. 2014, with a larger number of spectra (813 observations of 666 stars) and with a more extended wavelength coverage as the data from the near-infrared arm of the X-Shooter spectrograph are now included. The DR2 spectra then consist of three segments that were observed simultaneously and, if combined, cover the range between $\sim$300 nm and $\sim$2.45 $\mu$m at a spectral resolving power close to $R=10\,000$. The spectra were corrected for instrument transmission and telluric absorption, and they were also corrected for wavelength-dependent flux-losses in 85% of the cases. On average, synthesized broad-band colors agree with those of the MILES library and of the combined IRTF and Extended IRTF libraries to within $\sim\!1$%. The scatter in these comparisons indicates typical errors on individual colors in the XSL of 2$-$4 %. The comparison with 2MASS point source photometry shows systematics of up to 5% in some colors, which we attribute mostly to zero-point or transmission curve errors and a scatter that is consistent with the above uncertainty estimates. The final spectra were corrected for radial velocity and are provided in the rest-frame (with wavelengths in air). The spectra cover a large range of spectral types and chemical compositions (with an emphasis on the red giant branch), which makes this library an asset when creating stellar population synthesis models or for the validation of near-ultraviolet to near-infrared theoretical stellar spectra across the Hertzsprung-Russell diagram.

The Fornax 3D project: Non-linear colour-metallicity relation of globular clusters

Abstract: Globular cluster (GC) systems of massive galaxies often show a bimodal colour distribution. This has been interpreted as a metallicity bimodality, created by a two-stage galaxy formation where the red, metal-rich GCs were formed in the parent halo and the blue metal-poor GCs were accreted. This interpretation, however, crucially depends on the assumption that GCs are exclusively old stellar systems with a linear colour–metallicity relation (CZR). The shape of the CZR and range of GC ages are currently under debate because their study requires high quality spectra to derive reliable stellar population properties. We determined metallicities with full spectral fitting from a sample of 187 GCs with a high spectral signal-to-noise ratio in 23 galaxies of the Fornax cluster that were observed as part of the Fornax 3D project. The derived CZR from this sample is non-linear and can be described by a piecewise linear function with a break point at (g −z ) ∼ 1.1 mag. The less massive galaxies in our sample (M * M ⊙ ) appear to have slightly younger GCs, but the shape of the CZR is insensitive to the GC ages. Although the least massive galaxies lack red, metal-rich GCs, a non-linear CZR is found irrespective of the galaxy mass, even in the most massive galaxies (M * ≥ 1011 M ⊙ ). Our CZR predicts narrow unimodal GC metallicity distributions for low mass and broad unimodal distributions for very massive galaxies, dominated by a metal-poor and metal-rich peak, respectively, and bimodal distributions for galaxies with intermediate masses (1010 ≤ M * M ⊙ ) as a consequence of the relative fraction of red and blue GCs. The diverse metallicity distributions challenge the simple differentiation of GC populations solely based on their colour.

Disentangling the formation history of galaxies via population-orbit superposition: method validation

Abstract: We present population-orbit superposition models for external galaxies based on Schwarzschild's orbit-superposition method, by tagging the orbits with age and metallicity. The models fit the density distributions, as well as kinematic, age and metallicity maps from Integral Field Unit (IFU) spectroscopy observations. We validate the method and demonstrate its power by applying it to mock data, similar to those obtained by the Multi-Unit Spectroscopic Explorer (MUSE) IFU on the Very Large Telescope (VLT). These mock data are created from Auriga galaxy simulations, viewed at three different inclination angles ($\vartheta=40^o, 60^o, 80^o$). Constrained by MUSE-like mock data, our model can recover the galaxy's stellar orbit distribution projected in orbital circularity $\lambda_z$ vs. radius $r$, the intrinsic stellar population distribution in age $t$ vs. metallicity $Z$, and the correlation between orbits' circularity $\lambda_z$ and stellar age $t$. A physically motivated age-metallicity relation improves recovering the intrinsic stellar population distributions. We decompose galaxies into cold, warm and hot + counter-rotating components based on their orbit circularity distribution, and find that the surface density, mean velocity, velocity dispersion, age and metallicity maps of each component from our models well reproduce those from simulation, especially for projections close to edge-on. These galaxies exhibit strong global age vs. $\sigma_z$ relation, which is well recovered by our model. The method has the power to reveal the detailed build-up of stellar structures in galaxies, and offers a complement to local resolved, and high-redshift studies of galaxy evolution.

Stellar populations across galaxy bars in the MUSE TIMER project

Abstract: Stellar populations in barred galaxies save an imprint of the influence of the bar on the host galaxy's evolution. We present a detailed analysis of star formation histories (SFHs) and chemical enrichment of stellar populations in nine nearby barred galaxies from the TIMER project. We used integral field observations with the MUSE instrument to derive unprecedented spatially resolved maps of stellar ages, metallicities, [Mg/Fe] abundances, and SFHs, as well as Hα as a tracer of ongoing star formation. We find a characteristic V-shaped signature in the SFH that is perpendicular to the bar major axis, which supports the scenario where intermediate-age stars (∼2?- 6 Gyr) are trapped on more elongated orbits shaping a thinner part of the bar, while older stars (> 8 Gyr) are trapped on less elongated orbits shaping a rounder and thicker part of the bar. We compare our data to state-of-the-art cosmological magneto-hydrodynamical simulations of barred galaxies and show that such V-shaped SFHs arise naturally due to the dynamical influence of the bar on stellar populations with different ages and kinematic properties. Additionally, we find an excess of very young stars (< 2 Gyr) on the edges of the bars, predominantly on the leading side, thus confirming typical star formation patterns in bars. Furthermore, mass-weighted age and metallicity gradients are slightly shallower along the bar than in the disc, which is likely due to orbital mixing in the bar. Finally, we find that bars are mostly more metal-rich and less [Mg/Fe]-enhanced than the surrounding discs. We interpret this as a signature that the bar quenches star formation in the inner region of discs, usually referred to as star formation deserts. We discuss these results and their implications on two different scenarios of bar formation and evolution.

Kinematic analysis of EAGLE simulations: Evolution of ${\lambda}_{Re}$ and its connection with mergers and gas accretion

Abstract: We have developed a new tool to analyse galaxies in the EAGLE simulations as close as possible to observations.We investigated the evolution of their kinematic properties by means of the angular momentum proxy parameter,$ \lambda_{Re} $for galaxies with $M_{*} \ge 5 \times 10^{9} M_{\odot}$ in the RefL0100N1504 simulation up to redshift two (z = 2). Galaxies in the simulation show a wide variety of kinematic features, similiar to those found in integral-field spectroscopic studies. At z=0 the distribution of galaxies in the ${\lambda}_{Re}-{\epsilon}$ plane is also in good agreement with results from observations. Scaling relations at z = 0 indicate that there is critical mass, $M_{crit} = 10^{10.3} M_{\odot}$, that divides two different regimes when we include the ${\lambda}_{Re}$ parameter. The simulation shows that the distribution of galaxies in the ${\lambda}_{Re}-{\epsilon}$ plane evolves with time until z = 2 when galaxies are equally distributed both in ${\lambda}_{Re}$ and ${\epsilon}$. We studied the evolution of ${\lambda}_{Re}$ with time and found that there is no connection between the angular momentum at z = 2 and z = 0. All systems reach their maximum ${\lambda}_{Re}$ at z = 1 and then steadily lose angular momentum regardless of their merger history, except for the high star-forming systems that sustain that maximum value over time. The evolution of the Re in galaxies that have not experienced any merger in the last 10 Gyr can be explained by their level of gas accretion.

The Fornax 3D project: Non-linear colour-metallicity relation of globular clusters

Abstract: Globular cluster (GC) systems of massive galaxies often show a bimodal colour distribution. This has been interpreted as a metallicity bimodality, created by a two-stage galaxy formation where the red, metal-rich GCs were formed in the parent halo and the blue metal-poor GCs were accreted. This interpretation, however, crucially depends on the assumption that GCs are exclusively old stellar systems with a linear colour-metallicity relation (CZR). The shape of the CZR and range of GC ages are currently under debate, because their study requires high quality spectra to derive reliable stellar population properties. We determined metallicities with full spectral fitting from a sample of 187 GCs with high spectral signal-to-noise ratio in 23 galaxies of the Fornax cluster that were observed as part of the Fornax 3D project. The derived CZR from this sample is non-linear and can be described by a piecewise linear function with a break point at ($g - z$) $\sim$ 1.1 mag. The less massive galaxies in our sample ($M_\ast < 10^{10} M_\odot$) appear to have slightly younger GCs, but the shape of the CZR is insensitive to the GC ages. Although the least massive galaxies lack red, metal-rich GCs, a non-linear CZR is found irrespective of the galaxy mass, even in the most massive galaxies ($M_\ast \geq 10^{11} M_\odot$). Our CZR predicts narrow unimodal GC metallicity distributions for low mass and broad unimodal distributions for very massive galaxies, dominated by a metal-poor and metal-rich peak, respectively, and bimodal distributions for galaxies with intermediate masses (10$^{10}$ $\leq$ $M_\ast < 10^{11} M_\odot$) as a consequence of the relative fraction of red and blue GCs. The diverse metallicity distributions challenge the simple differentiation of GC populations solely based on their colour.

The Fornax Deep Survey with VST. VIII. Connecting the accretion history with the cluster density

Abstract: This work is based on deep multi-band (g, r, i) data from the Fornax Deep Survey with VST. We analyse the surface brightness profiles of the 19 bright ETGs inside the virial radius of the Fornax cluster. The main aim of this work is to identify signatures of accretion onto galaxies by studying the presence of outer stellar halos, and understand their nature and occurrence. Our analysis also provides a new and accurate estimate of the intra-cluster light inside the virial radius of Fornax. We performed multi-component fits to the azimuthally averaged surface brightness profiles available for all sample galaxies. This allows to quantify the relative weight of all components in the galaxy structure that contribute to the total light. In addition, we derived the average g-i colours in each component identified by the fit, as well as the azimuthally averaged g-i colour profiles, to correlate them with the stellar mass of each galaxy and the location inside the cluster. We find that in the most massive and reddest ETGs the fraction of light in, probably accreted, halos is much larger than in the other galaxies. Less-massive galaxies have an accreted mass fraction lower than 30%, bluer colours and reside in the low-density regions of the cluster. Inside the virial radius of the cluster, the total luminosity of the intra-cluster light, compared with the total luminosity of all cluster members, is about 34%. Inside the Fornax cluster there is a clear correlation between the amount of accreted material in the stellar halos of galaxies and the density of the environment in which those galaxies reside. By comparing this quantity with theoretical predictions and previous observational estimates, there is a clear indication that the driving factor for the accretion process is the total stellar mass of the galaxy, in agreement with the hierarchical accretion scenario.

The SAMI–Fornax Dwarfs Survey I: sample, observations, and the specific stellar angular momentum of dwarf elliptical galaxies

Abstract: Dwarf ellipticals are the most common galaxy type in cluster environments; however, the challenges associated with their observation mean that their formation mechanisms are still poorly understood. To address this, we present deep integral field observations of a sample of 31 low-mass (10(7.5) < M-* < 10(9.5) M-circle dot) early-type galaxies in the Fornax cluster with the SAMI instrument. For 21 galaxies, our observations are sufficiently deep to construct spatially resolved maps of the stellar velocity and velocity dispersion - for the remaining galaxies, we extract global velocities and dispersions from aperture spectra only. From the kinematic maps, we measure the specific stellar angular momentum lambda(R) of the lowest mass dE galaxies to date. Combining our observations with early-type galaxy data from the literature spanning a large range in stellar mass, we find that lambda(R) decreases towards lower stellar mass, with a corresponding increase in the proportion of slowly rotating galaxies in this regime. The decrease of lambda(R) with mass in our sample dE galaxies is consistent with a similar trend seen in somewhat more massive spiral galaxies from the CALIFA survey. This suggests that the degree of dynamical heating required to produce dEs from low-mass starforming progenitors may be relatively modest and consistent with a broad range of formation mechanisms.

On the accretion of a new group of galaxies on to Virgo: I. Internal kinematics of nine in-falling dEs

Abstract: Galaxy environment has been shown to play an important role in transforming late-type, star-forming galaxies to quiescent spheroids. This transformation is expected to be more severe for low-mass galaxies ( $M \lt 10^{10}\, \mathrm{M}_\odot$ ) in dense galaxy groups and clusters, mostly due to the influence of their past host haloes (also known as pre-processing) and their present-day environments. For the first time, in this study, we investigate a sample of nine early-type dwarf galaxies (dEs) that were accreted as a likely bound group on to the Virgo galaxy cluster about 2-3 Gyr ago. Considering this special condition, these nine dEs may provide a test bed for distinguishing between the influence of the Virgo galaxy cluster and the effects of the previous host halo on their current properties. Specifically, we use VLT/MUSE integral-field unit spectra to derive their kinematics and specific angular momentum (λR) profiles. We observe a spread in the λR profiles of our sample dEs, finding that the λR profiles of half of them are as high as those of low-mass field galaxies. The remaining dEs exhibit λR profiles as low as those of Virgo dEs that were likely accreted longer ago. Moreover, we detect nebular emission in one dE with a gas velocity offset suggesting ongoing gas stripping in Virgo. We suggest that the low-λR dEs in our sample were processed by their previous host halo, prior to their infall to Virgo, and that the high-λR dEs may be experiencing ram pressure stripping in Virgo.

NIHAO XXIV: rotation- or pressure-supported systems? Simulated Ultra Diffuse Galaxies show a broad distribution in their stellar kinematics

Abstract: In recent years, a new window on galaxy evolution opened, thanks to the increasing discovery of galaxies with a low-surface brightness, such as Ultra Diffuse Galaxies (UDGs). The formation mechanism of these systems is still a much debated question and so are their kinematical properties. In this work, we address this topic by analysing the stellar kinematics of isolated UDGs formed in the hydrodynamical simulation suite Numerical Investigation of a Hundred Astrophysical Objects (NIHAO). We construct projected line-of-sight velocity and velocity dispersion maps to compute the projected specific angular momentum, λR, to characterize the kinematical support of the stars in these galaxies. We found that UDGs cover a broad distribution, ranging from dispersion to rotation-supported galaxies, with similar abundances in both regimes. The degree of rotation support of simulated UDGs correlates with several properties such as galaxy morphology, higher H i fractions, and larger effective radii with respect to the dispersion-supported group, while the dark matter halo spin and mass accretion history are similar among the two populations. We demonstrate that the alignment of the infalling baryons into the protogalaxy at early z is the principal driver of the z = 0 stellar kinematic state: pressure-supported isolated UDGs form via misaligned gas accretion while rotation-supported ones build up their baryons in an ordered manner. Accounting for random inclination effects, we predict that a comprehensive survey will find nearly half of field UDGs to have rotationally supported stellar discs, when selecting UDGs with effective radius larger than 1 kpc.

The Fornax Deep Survey (FDS) with VST. VI. Optical properties of the dwarf galaxies in the Fornax cluster (Corrigendum)

Abstract: Aku Venhola1,2, Reynier Peletier2, Eija Laurikainen1, Heikki Salo1, Enrichetta Iodice3, Steffen Mieske4, Michael Hilker5, Carolin Wittmann6, Maurizio Paolillo7,3, Michele Cantiello8, Joachim Janz1,13, Marilena Spavone3, Raffaele D’Abrusco9, Glenn van de Ven14, Nicola Napolitano3, Gijs Verdoes Kleijn2, Massimo Capaccioli10, Aniello Grado3, Edwin Valentijn2, Jesús Falcón-Barroso11,12, and Luca Limatola3

The Fornax Deep Survey with VST : X. The assembly history of the bright galaxies and intra-group light in the Fornax A subgroup

Abstract: Context. We present the study of the south-west group in the Fornax cluster centred on the brightest group galaxy (BGG) Fornax A, which was observed as part of the Fornax Deep Survey (FDS). This includes the analysis of the bright group members (m B The main objective of this work is to investigate the assembly history of the Fornax A group and to compare its physical quantities as a function of the environment to that of the Fornax cluster core.Methods. For all galaxies, we extracted the azimuthally averaged surface brightness profiles in three optical bands (g , r , i ) by modelling the galaxy’s isophotes. We derived their colour (g − i ) profiles, total magnitude, effective radius in all respective bands, stellar mass, and the break radius in the r -band. The long integration time and large covered area of the FDS allowed us to also estimate the amount of IGL.Results. The majority of galaxies in the Fornax A group are late-type galaxies (LTGs), spanning a range of stellar mass of 8 * M ⊙ ) L ⊙ in the g -band, which corresponds to about 16% of the total light in the group.Conclusions. The Fornax A group appears to be in an early-stage of assembly with respect to the cluster core. The environment of the Fornax A group is not as dense as that of the cluster core, with all galaxies except the BGG showing similar morphology, comparable colours and stellar masses, and Type III disc-breaks, without any clear trend in these properties with group-centric distances. The low amount of IGL is also consistent with this picture, since there were no significant gravitational interactions between galaxies that modified the galaxies’ structure and contributed to the build-up of the IGL. The main contribution to the IGL is from the minor merging in the outskirts of the BGG NGC 1316 and, probably, the disrupted dwarf galaxies close to the group centre.

Fornax 3D project: Automated detection of planetary nebulae in the centres of early-type galaxies and first results

Abstract: Extragalactic planetary nebulae (PNe) are detectable through relatively strong nebulous [O III] emission and act as direct probes into the local stellar population. Because they have an apparently universal invariant magnitude cut-off, PNe are also considered to be a remarkable standard candle for distance estimation. Through detecting PNe within the galaxies, we aim to connect the relative abundances of PNe to the properties of their host galaxy stellar population. By removing the stellar background components from FCC 167 and FCC 219, we aim to produce PN luminosity functions (PNLF) of these galaxies, and thereby also estimate the distance modulus to these two systems. Finally, we test the reliability and robustness of our novel detection and analysis method. It detects unresolved point sources by their [O III] 5007 A emission within regions that have previously been unexplored. We model the [O III] emissions in the spatial and spectral dimensions together, as afforded to us by the Multi Unit Spectroscopic Explorer, and we draw on data gathered as part of the Fornax3D survey. For each source, we inspect the properties of the nebular emission lines to remove other sources that might hinder the safe construction of the PNLF, such as supernova remnants and H II regions. As a further step, we characterise any potential limitations and draw conclusions about the reliability of our modelling approach through a set of simulations. By applying this novel detection and modelling approach to integral field unit observations, we report for the distance estimates and luminosity-specific PNe frequency values for the two galaxies. Furthermore, we include an overview of source contamination, galaxy differences, and possible effects on the PNe populations in the dense stellar environments.

Globular cluster ejection, infall, and the host dark matter halo of the Pegasus dwarf galaxy

Abstract: Recent photometric observations revealed a massive, extended (MGC ≳ 105 M⊙; Rh ∼ 14 pc) globular cluster (GC) in the central region (D3D ≲ 100 pc) of the low-mass (M* ∼ 5 × 106 M⊙) dwarf irregular galaxy Pegasus. This massive GC offers a unique opportunity to study star cluster inspiral as a mechanism for building up nuclear star clusters, and the dark matter (DM) density profile of the host galaxy. Here, we present spectroscopic observations indicating that the GC has a systemic velocity of ΔV = 3 ± 8 km s−1 relative to the host galaxy, and an old, metal-poor stellar population. We run a suite of orbital evolution models for a variety of host potentials (cored to cusped) and find that the GC’s observed tidal radius (which is ∼3 times larger than the local Jacobi radius), relaxation time, and relative velocity are consistent with it surviving inspiral from a distance of Dgal ≳ 700 pc (up to the maximum tested value of Dgal = 2000 pc). In successful trials, the GC arrives to the galaxy centre only within the last ∼1.4 ± 1 Gyr. Orbits that arrive in the centre and survive are possible in DM haloes of nearly all shapes, however to satisfy the GC’s structural constraints a galaxy DM halo with mass MDM ≃ 6 ± 2 × 109 M⊙, concentration c ≃ 13.7 ± 0.6, and an inner slope to the DM density profile of −0.9 ≤ γ ≤ −0.5 is preferred. The gas densities necessary for its creation and survival suggest the GC could have formed initially near the dwarf’s centre, but then was quickly relocated to the outskirts where the weaker tidal field permitted an increased size and relaxation time – with the latter preserving the former during subsequent orbital decay.

Stellar populations across galaxy bars in the MUSE TIMER project

Abstract: Stellar populations in barred galaxies save an imprint of the influence of the bar on the host galaxy's evolution. We present a detailed analysis of star formation histories (SFHs) and chemical enrichment of stellar populations in nine nearby barred galaxies from the TIMER project. We use integral field observations with the MUSE instrument to derive unprecedented spatially resolved maps of stellar ages, metallicities, [Mg/Fe] abundances and SFHs, as well as H$\alpha$ as a tracer of ongoing star formation. We find a characteristic V-shaped signature in the SFH perpendicular to the bar major axis which supports the scenario where intermediate age stars ($\sim 2$-$6\ \mathrm{Gyr}$) are trapped on more elongated orbits shaping a thinner part of the bar, while older stars ($> 8\ \mathrm{Gyr}$) are trapped on less elongated orbits shaping a rounder and thicker part of the bar. We compare our data to state-of-the-art cosmological magneto-hydrodynamical simulations of barred galaxies and show that such V-shaped SFHs arise naturally due to the dynamical influence of the bar on stellar populations with different ages and kinematic properties. Additionally, we find an excess of very young stars ($< 2\ \mathrm{Gyr}$) on the edges of the bars, predominantly on the leading side, confirming typical star formation patterns in bars. Furthermore, mass-weighted age and metallicity gradients are slightly shallower along the bar than in the disc likely due to orbital mixing in the bar. Finally, we find that bars are mostly more metal-rich and less [Mg/Fe]-enhanced than the surrounding discs. We interpret this as a signature that the bar quenches star formation in the inner region of discs, usually referred to as star formation deserts. We discuss these results and their implications on two different scenarios of bar formation and evolution.

BAYES-LOSVD: a bayesian framework for non-parametric extraction of the line-of-sight velocity distribution of galaxies

Abstract: We introduce BAYES-LOSVD, a novel implementation of the non-parametric extraction of line-of-sight velocity distributions (LOSVDs) in galaxies. We employ bayesian inference to obtain robust LOSVDs and associated uncertainties. Our method relies on principal component analysis to reduce the dimensionality of the base of templates required for the extraction and thus increase the performance of the code. In addition, we implement several options to regularise the output solutions. Our tests, conducted on mock spectra, confirm the ability of our approach to model a wide range of LOSVD shapes, overcoming limitations of the most widely used parametric methods (e.g. Gauss-Hermite expansion). We present examples of LOSVD extractions for real galaxies with known peculiar LOSVD shapes, i.e. NGC4371, IC0719 and NGC4550, using MUSE and SAURON integral-field unit (IFU) data. Our implementation can also handle data from other popular IFU surveys (e.g. ATLAS3D, CALIFA, MaNGA, SAMI). Details of the code and relevant documentation are freely available to the community in the dedicated repositories.

The kinematics of young and old stellar populations in nuclear rings of MUSE TIMER galaxies

Abstract: Context. Studying the stellar kinematics of galaxies is a key tool in the reconstruction of their evolution. However, the current measurements of the stellar kinematics are complicated by several factors, including dust extinction and the presence of multiple stellar populations. Aims. We use integral field spectroscopic data of four galaxies from the Time Inference with MUSE in Extragalactic Rings (TIMER) survey to explore and compare the kinematics measured in different spectral regions that are sensitive to distinct stellar populations. Methods.We derive the line-of-sight velocity and velocity dispersion of both a young (.2 Gyr) and an old stellar population from the spectral regions around the Hβ line and the Ca II Triplet. In addition, we determine colour excess, mean age, and metallicity. Results. We report a correlation of the colour excess with the difference in the kinematic parameters of the Hβ line and the Ca II Triplet range, which are dominated by young and old stellar populations, respectively. Young stellar populations, located primarily in nuclear rings, have higher velocity dispersions than old ones. These differences in the rings are typically ∼10 km s-1 in velocity dispersion but can have a mean value as high as ≈24 km s-1 in the most extreme case. Trends with age exist in the nuclear rings but are less significant than those with dust extinction. We report different degrees of correlation for these trends among the galaxies in the sample, which are related to the size of the Voronoi bins in their rings. No clear trends for the line-of-sight velocity differences are observed. The absence of these trends can be explained as a consequence of the Hβ line masking process during the kinematic extraction, as confirmed by dedicated simulations. Conclusions. Our study demonstrates that kinematic differences caused by different stellar populations can be identified in the central regions of nearby galaxies, even from intermediate resolution spectroscopy. This opens the door to future detailed chemo-kinematic studies of galaxies, but also serves as a warning against deriving kinematics from full-spectrum fitting across very wide wavelength ranges when intense star formation is taking place.

The Fornax 3D project: Globular clusters tracing kinematics and metallicities

Abstract: Globular clusters (GCs) are found ubiquitously in massive galaxies and due to their old ages, they are regarded as fossil records of galaxy evolution. Spectroscopic studies of GC systems are often limited to the outskirts of galaxies, where GCs stand out against the galaxy background and serve as bright tracers of galaxy assembly. In this work, we use the capabilities of the Multi Unit Explorer Spectrograph (MUSE) to extract a spectroscopic sample of 722 GCs in the inner regions ($\lesssim 3 R_\text{eff}$) of 32 galaxies in the Fornax cluster. These galaxies were observed as part of the Fornax 3D project, a MUSE survey that targets early and late-type galaxies within the virial radius of Fornax. After accounting for the galaxy background in the GC spectra, we extracted line-of-sight velocities and determined metallicities of a sub-sample of 238 GCs. We found signatures of rotation within GC systems, and comparing the GC kinematics and that of the stellar body shows that the GCs trace the spheroid of the galaxies. While the red GCs prove to closely follow the metallicity profile of the host galaxy, the blue GCs show a large spread of metallicities but they are generally more metal-poor than the host.

Galaxies within galaxies in the TIMER survey: stellar populations of inner bars are scaled replicas of main bars

Abstract: Inner bars are frequent structures in the local Universe and thought to substantially influence the nuclear regions of disc galaxies. In this study we explore the structure and dynamics of inner bars by deriving maps and radial profiles of their mean stellar population content and comparing them to previous findings in the context of main bars. To this end, we exploit observations obtained with the integral-field spectrograph MUSE of three double-barred galaxies in the TIMER sample. The results indicate that inner bars can be distinguished based on their stellar population properties alone. More precisely, inner bars show elevated metallicities and depleted [$\alpha$/Fe] abundances. Although they exhibit slightly younger stellar ages compared to the nuclear disc, the typical age differences are small, except at their outer ends. These ends of the inner bars are clearly younger compared to their inner parts, an effect known from main bars as orbital age separation. In particular, the youngest stars (i.e. those with the lowest radial velocity dispersion) seem to occupy the most elongated orbits along the (inner) bar major axis. We speculate that these distinct ends of bars could be connected to the morphological feature of ansae. Radial profiles of metallicity and [$\alpha$/Fe] enhancements are flat along the inner bar major axis, but show significantly steeper slopes along the minor axis. This radial mixing in the inner bar is also known from main bars and indicates that inner bars significantly affect the radial distribution of stars. In summary, based on maps and radial profiles of the mean stellar population content and in line with previous TIMER results, inner bars appear to be scaled down versions of the main bars seen in galaxies. This suggests the picture of a "galaxy within a galaxy", with inner bars in nuclear discs being dynamically equivalent to main bars in main galaxy discs.

Larger λR in the disc of isolated active spiral galaxies than in their non-active twins

Abstract: We present a comparison of the spin parameter λ R , measured in a region dominated by the galaxy disc, between 20 pairs of nearby (0.005 R than their corresponding non-active twin(s), indicating larger rotational support in the active galactic nuclei (AGN) discs. This result is driven by the 11 pairs of unbarred galaxies, for which 100% of the AGN show larger λ R than their twins. These results can be explained by a more efficient angular momentum transfer from the inflowing gas to the disc baryonic matter in the case of the active galaxies. This gas inflow could have been induced by disc or bar instabilities, although we cannot rule out minor mergers if these are prevalent in our active galaxies. This result represents the first evidence of galaxy-scale differences between the dynamics of active and non-active isolated spiral galaxies of intermediate stellar masses (1010 * M ⊙ ) in the Universe.

Fornax 3D project: automated detection of planetary nebulae in the centres of early-type galaxies and first results

Abstract: Extragalactic planetary nebulae (PNe) are detectable through relatively strong nebulous [OIII] emission and act as direct probes into the local stellar population. Because they have an apparently universal invariant magnitude cut-off, PNe are also considered to be a remarkable standard candle for distance estimation. Through detecting PNe within the galaxies, we aim to connect the relative abundances of PNe to the properties of their host galaxy stellar population. By removing the stellar background components from FCC 167 and FCC 219, we aim to produce PN luminosity functions (PNLF) of these galaxies, and thereby also estimate the distance modulus to these two systems. Finally, we test the reliability and robustness of our novel detection and analysis method. It detects unresolved point sources by their [OIII] 5007A emission within regions that have previously been unexplored. We model the [OIII] emissions in the spatial and spectral dimensions together, as afforded to us by the Multi Unit Spectroscopic Explorer (MUSE), and we draw on data gathered as part of the Fornax3D survey. For each source, we inspect the properties of the nebular emission lines to remove other sources that might hinder the safe construction of the PNLF, such as supernova remnants and HII regions. As a further step, we characterise any potential limitations and draw conclusions about the reliability of our modelling approach through a set of simulations. By applying this novel detection and modelling approach to integral field unit observations, we report for the distance estimates and luminosity-specific PNe frequency values for the two galaxies. Furthermore, we include an overview of source contamination, galaxy differences, and possible effects on the PNe populations in the dense stellar environments.

Detection of young (≤20 Myr) stellar populations in apparently quenched low-mass galaxies using red spectral line indices

Abstract: We report on the detection of a small contribution (around and below 1% in mass) from young stellar components with ages $\leq$20 Myr in low-mass galaxies purposely selected from the MaNGA survey to be already-quenched systems. Among the sample of 28 galaxies, eight of them show signatures of having suffered a very recent burst of star formation. The detection has been done through the analysis of line-strength indices in the red spectral range [5700,8800] A. The increasing contribution of red supergiants to this red regime is responsible for a deviation of the index measurements with respect to their position within the model grids in the standard spectral range [3600,5700] A. We demonstrate that a combination of red indices, as well as a qualitative assessment of the mean luminosity-weighted underlying stellar population, is required in order to distinguish between a true superyoung population and other possible causes of this deviation, such as abundance ratio variations. Our result implies that many presumably quenched low-mass galaxies actually contain gas that is triggering some level of star formation. They have, therefore, either accreted external gas, internally recycled enough gas from stellar evolution to trigger new star formation, or they kept a gas reservoir after the harassment or stripping process that quenched them in first place. Internal processes are favoured since we find no particular trends between our non-quenched galaxies and their environment, although more work is needed to fully discard an external influence.